1. Field of the Invention
The present invention relates to an ink jet printing apparatus to print an image using an ink ejection print head and a recovery method to keep an ink ejection performance of the print head in good condition.
2. Description of the Related Art
A recovery operation to keep the ink ejection from nozzle openings of the print head in normal condition has conventionally been performed in ink jet printing apparatus. The recovery operation can discharge viscous ink and minute ink bubbles from the print head and remove foreign matters and ink mist adhering to a surface of the print head where nozzle openings are formed. The recovery operation is known to include a suction operation, a preliminary ejection operation, a wiping operation and a heating operation, for example.
Ink bubbles, when formed in the nozzle openings of the print head in particular, may cause ink ejection anomalies, such as ink ejection failures, a deflection of ink ejecting direction and reduced ink ejection volumes. Such phenomena can be observed when a print head is applied small vibrations and impacts as it is mounted on an ink jet printing apparatus, and when it falls. In such cases, conventional recovery operation involves first sucking out ink bubbles from the nozzle openings of the print head and then executing a preliminary ejection.
The preliminary ejection operation is an operation to discharge residual ink and bubbles from the nozzle openings of the print head by ejecting ink not used for image printing out onto a predetermined location outside a print medium. The preliminary ejection operation following the suction operation is intended to remove color inks that are mixed together during the suction operation. The suction operation sucks out ink and bubbles from the nozzle openings of the print head by a negative pressure generated by a pump for example. During a general suction operation, the nozzle openings of the print head are hermetically closed by a cap into which a negative pressure is introduced to suck out ink and bubbles from the print head out into the cap. Japanese Patent Laid-Open No. 63-224958 discloses a method for suction operation which involves pressing an elastic cap against the nozzle opening-formed surface of the print head, increasing the pressure in the cap, releasing the interior of the cap to the open air and then introducing a negative pressure into the cap.
However, the suction operation to suck out bubbles from the nozzle openings of the print head as described above requires a suction mechanism such as a negative pressure pump, leading to increased complexity and cost of the apparatus as a whole. Further, in printing highly defined images such as photographs, a print head that ejects smaller volumes of ink is required. Such a print head has an increased flow resistance in ink paths communicating with the nozzle openings because of reduced cross sections of the ink paths. For the suction operation to be effectively performed on such a print head, therefore, the negative pressure introduced into the cap needs to be enhanced significantly to create a fast enough ink flow to suck out bubbles from the nozzle openings. The increased suction force necessarily increases the volume of waste ink sucked out of the nozzle openings, which in turn may reduce the volume of ink available for use in printing.
Japanese Patent Laid-Open No. 2002-160384 describes a heating operation as a recovery operation. The heating operation boils the ink in individual ink paths communicating to the nozzle openings by using heating elements. The heated ink inflates bubbles adhering to the common liquid chamber communicating with individual ink paths and thereby discharges the bubbles from the common liquid chamber out into an ink supply chamber.
Though it does not lead to an increased complexity of the apparatus as a whole as does the suction operation, or to a higher cost and an increased volume of waste ink, the above heating operation has exhibited a low level of performance in removing bubbles adhering to nozzle ends.